1. Field of the Invention
The present invention relates to a radio data communication technique which makes use of a circuit state notification function.
2. Description of the Related Art
Conventionally, in radio communication of a PHS (Personal Handyphone System) system or a PDC (Personal Digital Cellular) system, a radio circuit cannot be connected at such a place at which radio waves do not arrive or are less liable to arrive such as the inside of a tunnel, a location behind a building or an underground market. Therefore, a user is obliged, before communication is started, to look closely at a circuit state displayed on a radio unit (usually a circuit state is indicated by a number of antennae) and connect a radio circuit when the user determines that the radio state is good. Consequently, an operation for connection is very cumbersome.
In order to solve the problem described above, a method is proposed in Japanese Patent Application No. 78713/1998 wherein an electric field strength is acquired periodically from a radio unit and it is tried to connect a radio circuit when the acquired electric field strength exceeds a threshold value set in advance. Meanwhile, in the conventional MCPC (Mobile Computing Promotion Consortium), in order to realize the method described above, examinations have been started for interfaces among a radio unit, a terminal adapter and a portable terminal.
However, according to the method described above, in a situation wherein a circuit state is bad and unstable, acquisition of an electric field strength and discrimination of whether or not connection is possible are repeated until a good circuit state is obtained. Consequently, the method has a problem in that there is the possibility that the processing speed of the portable terminal may drop or the amounts of power consumption of the portable terminal and the radio unit may be increased by such repetition.